1. Field of the Invention
The present invention relates to a light source unit capable of preventing the deterioration of a luminescent material layer, an illumination method of this light source unit and a projector including the light source unit.
2. Description of the Related Art
In these days, data projectors are used on many occasions as an image projection unit which projects images including an image of a screen and a video image of a personal computer, as well as images based on image data which is stored in a memory card on to a screen. In these data projectors, light emitted from a light source is caused to converge to a micromirror display element called a DMD (Digital Micromirror Device) or a liquid crystal panel so that a color image is displayed on a screen.
Conventionally, the mainstream of these projectors has been those which utilize a high-intensity discharge lamp as a light source. In recent years, however, there have been made various developments on projectors which use, as a light source, a light emitting diode, a laser diode, an organic EL device or a luminescent material.
Additionally, in recent years, there have also been made various proposals on a light source unit having a light emitting diode as an excitation light source and a luminescent wheel in which a luminescent material layer which converts light such as ultraviolet light emitted from the excitation light source as excitation light into visible light is formed on a transparent base.
In the present state in which the production of a light emitting diode is difficult which can emit highly bright light of a range of green wavelengths as a light source for the projectors described above, Japanese Unexamined Patent Publication No. 2011-53323 discloses a projector which utilizes a light source unit which emits highly bright light of a range of green wavelengths by using a green light emitting luminescent material and a small and high-output laser diode as an excitation light source. As a result, the projector can project a clear image on a screen even in a bright room.
In addition, the applicant of this patent application has proposed various light source units in which a luminescent material is used as a light emitting material which emits light by using a laser beam as excitation light. In some of the light source units, a diffuse transmission area where excitation light is transmitted and a light emitting area where luminous light is emitted by a luminescent material are formed on a rotational member, whereby a pencil of highly bright light having high in-plane uniformity can be emitted.
In the light source unit in which the diffuse transmission area and the luminous light emitting area are provided on the rotational member, the utilization efficiency of the rotational member is not sufficient. Additionally, there are demands for a light source unit suitable for use in a projector which has a longer life or a wider range of applications.